Film forming device

ABSTRACT

A film-forming apparatus of the invention is a film-forming apparatus that includes: a processing container that defines a chamber, a pedestal arranged in the chamber, on which a substrate to be processed can be placed, a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes, a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead, and a showerhead-temperature controlling unit that controls a temperature of the showerhead.

FIELD OF THE INVENTION

This invention relates to a film-forming apparatus that forms a predetermined thin film onto a substrate to be processed by means of chemical vapor deposition process (CVD).

BACKGROUND ART

In a semiconductor-device manufacturing process, in order to fill holes between electric wirings formed on a semiconductor wafer as an object to be processed, or in order to provide barrier layers, a metal such as Ti, Al or Cu and/or a metal compound such as WSi, TiN or TiSi is deposited to form a thin film.

Conventionally, such thin film of the metal or metal compound is deposited by means of physical vapor deposition process (PVD). However, recently, it is requested to make devices micro and highly integrated, so that design-rule is especially severe. Thus, it is difficult to obtain sufficient properties by PVD, which is inferior in filling performance. Then, such thin film starts to be deposited by CVD, which we can expect forms a film of better quality.

As a conventional CVD film-forming apparatus, an apparatus for forming a Ti film is explained as an example. In the CVD film-forming apparatus for forming a Ti film, a pedestal, in which a heater is embedded and onto which a semiconductor wafer is placed, is arranged in a chamber having another heater. A showerhead for discharging a process gas is provided above and opposite to the pedestal. The chamber is heated to a predetermined temperature, and the inside of the chamber is vacuumed to a predetermined vacuum level. Then, the semiconductor wafer placed on the pedestal is heated to a predetermined temperature, while the process gas such as TiCl₄, H₂ and the like is supplied from the showerhead. In addition, a high-frequency electric power is applied to the showerhead, so that the process gas is changed to plasma thereof. Then, the film-forming process is conducted.

However, recently, the semiconductor wafer starts to be enlarged to 300 mm. Thus, the film-forming apparatus has to be enlarged correspondingly. Therefore, the following problems appear manifestly.

When the temperature of the heater embedded in the pedestal rises up, the showerhead provided opposed to the pedestal is heated by radiant heat thereof. However, when the unit is enlarged, the showerhead is also enlarged, that is, heat capacity thereof becomes larger, so that it takes a longer time for the temperature to become stable when the showerhead is heated. That is, the throughput is deteriorated. If the temperature of the showerhead, that is, the surface temperature of the showerhead is not stable during a process, the process is not uniformly conducted. In addition, the conventional showerhead has a structure with high heat-insulating properties, in order to secure temperature stability during a process. Thus, if the showerhead is enlarged, it takes also a longer time to lower the temperature to a predetermined temperature, for example for a cleaning process. If the cleaning process is conducted under a high-temperature state, the showerhead member may be damaged.

In addition, during an idling state, the temperature of the pedestal has to be set higher than that during the process, in order to maintain the temperature of the showerhead at a predetermined temperature. This is explained in detail. Conventionally, during the plasma process, the temperatures of members in the chamber are raised by the plasma. Especially, the surface temperature of the showerhead tends to be raised because it has a large area opposed to the wafer surface and exposed to the plasma. However, when a film-forming process is conducted after an idling state or a cleaning process, it is possible that a film-forming rate for the first wafer is low. It is thought that the reason is that the temperature of the showerhead is low. That is, the temperature thereof is about 500° C. during a normal film-forming process, but it is thought that the temperature falls down by about 20 to 30° C. In order to prevent this, during the idling state or the cleaning process, the temperature of the pedestal had to be set higher than the film-forming temperature.

Furthermore, conventionally, at a maintenance process of the showerhead, an upper lid including the showerhead is opened by a degree not larger than 90 degrees, and then the showerhead is removed or the like. However, as the film-forming apparatus is enlarged, when the showerhead is also bulked or enlarged, it is difficult to conduct the maintenance process of the showerhead in accordance with the conventional method.

SUMMARY OF THE INVENTION

This invention is intended to solve the above problems. The object of this invention is to provide a film-forming apparatus that can lead a showerhead to a predetermined temperature within a short time and wherein temperature stability of the showerhead is high, and to provide a film-forming apparatus wherein maintenance of the showerhead can be easily conducted.

This invention is a film-forming apparatus comprising: a processing container that defines a chamber; a pedestal arranged in the chamber, on which a substrate to be processed can be placed; a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes; a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead; and a showerhead-temperature controlling unit that controls a temperature of the showerhead.

According to the invention, since the showerhead is provided with the temperature controlling unit, the showerhead can be actively controlled to a desired temperature, when the showerhead is heated. Thus, even if the film-forming apparatus is larger, the temperature of the showerhead can be raised and lowered within a short time. In addition, by actively controlling the temperature of the showerhead, temperature stability of the showerhead can be enhanced.

Furthermore, for example in a case of Ti-film-forming apparatus, when a pre-coated film is formed on the showerhead or the like before a process to the substrate to be processed, or when a Ti film is formed on the substrate to be processed, the film is also formed (deposited) on a surface of the showerhead. At that time, in order to form a stable film on the surface of the showerhead, Ticl_(x), which is generated by an intermediate reaction, has to be volatilized. Thus, the showerhead has to be heated over 425° C., in particular over 500° C. In a conventional art, it takes a long time to heat the showerhead, and it is uncertain whether the showerhead is at a desired temperature, so that such a stable film may not be generated. However, by providing the temperature-controlling unit in the showerhead, the showerhead can be controlled to a desired temperature during a film-forming process or a pre-coating process, so that a stable film can be surely formed on the showerhead. Therefore, the first film-forming process can be stably conducted.

Preferably, the processing container is formed in such a manner that the processing container can be vacuumed.

In addition, preferably, the film-forming apparatus further comprises a heating unit that heats the pedestal.

In addition, preferably, the showerhead has: a chamber-inside part that includes a surface in which the large number of gas-discharging holes appear; and an atmosphere-side part that contacts with atmospheric air outside the chamber; and the showerhead-temperature controlling unit is provided in the atmosphere-side part.

In the case, the showerhead-temperature controlling unit can be handled in the atmospheric air.

In addition, preferably, the film-forming apparatus further comprises a second heating unit that heats the chamber.

In addition, preferably, the showerhead-temperature controlling unit includes: a heating mechanism that heats the showerhead; a cooling mechanism that cools the showerhead; a temperature-detecting mechanism that detects a temperature of the showerhead; and a controller that controls at least the heating mechanism, based on a result detected by the temperature-detecting mechanism.

In the case, the showerhead can be rapidly controlled to a desired temperature when the showerhead is both heated and cooled.

In addition, in the case, more preferably, the heating mechanism has: an inside heater that heats an inside portion of the showerhead; and an outside heater that heats an outside portion of the showerhead; and the temperature detecting mechanism has: an inside-temperature detecting part that detects a temperature of the inside portion; and an outside-temperature detecting part that detects a temperature of the outside portion.

In the case, more preferably, the controller is adapted to control the inside heater in such a manner that a value detected by the inside-temperature detecting part coincides with a set temperature, and to control the outside heater in such a manner that a difference between a value detected by the outside-temperature detecting part and the value detected by the inside-temperature detecting part coincides with zero.

In the case, heat dissipation from the outside portion of the showerhead can be inhibited, so that more accurate temperature control can be achieved.

In addition, preferably, a thermal-insulating member is arranged on a surface of the showerhead reverse to the chamber.

In the case, during the process, heat dissipation from the showerhead can be effectively inhibited.

In addition, preferably, the showerhead has: a showerhead body; and a circular supporting part continued upward from on an outside periphery of the showerhead body; and the supporting part has a rib structure.

In the case, since the portion of the supporting part other than the rib structure can be made thin, heat dissipation from the supporting part can be reduced. Thus, temperature controlling performance can be more enhanced.

In the case, more preferably, an insulating member is arranged on the showerhead body and inside the supporting part.

In addition, preferably, a circular infilling member and a fixing member for fixing the infilling member to the showerhead or the processing container are arranged between the showerhead and the processing container.

In the case, more preferably, a resilient member is interposed between the infilling member and the fixing member. In the case, even when quartz, ceramics and so on is used as the infilling member, it can be prevented that the infilling member is damaged. In addition, by means of the resilient member, the interval between the infilling member and the fixing member can be made uniform.

In addition, preferably, the film-forming apparatus further comprises a plasma-generating unit for generating plasma of the process gas in the chamber.

In addition, preferably, the film-forming apparatus further comprises an inverting mechanism that inverts the showerhead by turning the showerhead outwardly from the chamber.

In the case, the showerhead is turned outwardly from the chamber, and thus inverted, so that the showerhead can be taken out from the chamber substantially completely. Thus, maintenance of the showerhead can be conducted very easily.

In addition, this invention is a film-forming apparatus comprising: a processing container that defines a chamber; a pedestal arranged in the chamber, on which a substrate to be processed can be placed; a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes; a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead; and an inverting mechanism that inverts the showerhead by turning the showerhead outwardly from the chamber.

According to the invention, the showerhead is turned outwardly from the chamber, and thus inverted, so that the showerhead can be taken out from the chamber substantially completely. Thus, maintenance of the showerhead can be conducted very easily.

Preferably, a circular infilling member and a fixing member for fixing the infilling member to the showerhead or the processing container are arranged between the showerhead and the processing container.

In the case, more preferably, a resilient member is interposed between the infilling member and the fixing member. In the case, even when quartz, ceramics and so on is used as the infilling member, it can be prevented that the infilling member is damaged. In addition, by means of the resilient member, the clearance between the infilling member and the fixing member can be made uniform.

More preferably, the fixing member is outwardly removable in a state wherein the showerhead is inverted, and the infilling member is upwardly removable in a state wherein the fixing member has been outwardly removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a CVD film-forming apparatus of an embodiment according to the present invention;

FIG. 2 is a plan view showing an upper portion of the showerhead of the CVD film-forming apparatus of the embodiment according to the present invention;

FIG. 3 is an enlarged sectional view showing a filler portion of the apparatus of FIG. 1;

FIG. 4 is a schematic view showing a portion corresponding to a heating mechanism in a temperature-controlling unit of the apparatus of FIG. 1;

FIG. 5 is a schematic view showing a preferable control manner in heating and controlling by means of the temperature-controlling unit of the apparatus of FIG. 1;

FIG. 6 is a sectional view showing a state wherein a showerhead of the apparatus of FIG. 1 is inverted by an inverting mechanism;

FIG. 7 is an enlarged view of the showerhead of the apparatus of FIG. 1;

FIG. 8 is a sectional view taken along A-A line of FIG. 7;

FIG. 9 is a sectional view taken along B-B line of FIG. 7;

FIG. 10 is a plan view showing a lower plate wherein a gas-diffusion-promoting pipe is provided;

FIG. 11 is a sectional view of the lower plate and a middle plate wherein the gas-diffusion-promoting pipe of FIG. 10 is attached;

FIG. 12 is a schematic view showing a variant of the portion corresponding to a heating mechanism of FIG. 4;

FIG. 13 is a schematic view showing a variant of the control manner of FIG. 5;

FIG. 14 is a sectional view showing a CVD film-forming apparatus of another embodiment according to the present invention; and

FIG. 15 is a sectional view showing a variant of the filler member of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a CVD film-forming apparatus for forming a Ti thin film according to an embodiment of the present invention is explained concretely.

FIG. 1 is a sectional view showing the CVD film-forming apparatus for forming a Ti thin film according to the embodiment of the present invention. FIG. 2 is a plan view showing an upper portion of a showerhead of the CVD film-forming apparatus of FIG. 1. The film-forming apparatus 1 has a sealed chamber 2 of a substantially cylindrical shape or a box-like shape. A pedestal 3, on which a semiconductor wafer W as an object to be processed is placed horizontally, is provided in the chamber 2. A pedestal supporting member 7 that protrudes downward is attached at a central bottom of the chamber 2 via a sealing ring. A cylindrical supporting member 4 joined to a bottom surface of the pedestal 3 is fixed to the pedestal supporting member 7. The chamber 2 and the pedestal supporting member 7 have heating mechanisms not shown. An electric power source not shown supplies electric power to the heating mechanisms, so that the chamber 2 and the pedestal supporting member 7 are heated to respective predetermined temperatures.

A ring 5 for stabilizing generation of plasma is provided at an outside peripheral portion of the pedestal 3. In addition, a heater 6 is embedded in the pedestal 3. An electric power source not shown supplies electric power to the heater 6, so that the semiconductor wafer W placed on the pedestal 3 as an object to be processed is heated to a predetermined temperature.

A showerhead 10 is arranged opposite to the pedestal 3 at an upper portion of the chamber 2. The showerhead 10 has an upper plate 10 a, a middle plate 10 b and a lower plate 10 c. The plane shape of the showerhead 10 is a circle.

The upper plate 10 a has a horizontal portion 10 d that forms a showerhead body together with the middle plate 10 b and the lower plate 10 c, and a circular supporting portion or part 10 e (continued upward from on an outside periphery of the horizontal portion 10 d. The upper plate 10 a is generally concave. As shown in FIGS. 1 and 2, inside the supporting portion 10 e and shown extending radially inward from an interior surface of a cylindrical wall of concave upper plate 10 a, are ribs 10 f which are arranged toward the center of the showerhead 10 at regular distance. As the ribs 10 f are formed, while strength against heat deformation of the supporting portion 10 e and supporting strength of the supporting portion 10 e are enhanced, the other portion of the supporting portion 10 e can be made thin. Thus, heat dissipation from the showerhead 10 can be inhibited.

Preferably, each rib 10 f protrudes toward the center by 5 mm or more, in particular 10 mm or more. In addition, preferably, a width of each rib 10 f is 2 mm or more, in particular 5 mm or more. In addition, preferably, the ribs 10 f are arranged at regular distance.

The upper plate 10 a serves as a base member. An upper portion of an outside periphery of the circular concave middle plate 10 b is fixed to a lower portion of an outside periphery of the horizontal portion 10 d of the upper plate 10 a by means of screws. An upper surface of the lower plate 10 c is fixed to a lower surface of the middle plate 10 b by means of screws. A space (e.g., a “first space”) 11 a is hermetically formed between a lower surface of the horizontal portion 10 d of the upper plate 10 a and an upper surface of the middle plate 10 b having a concave portion. A plurality of grooves are formed radially and uniformly in the lower surface of the middle plate 10 b. The middle plate 10 b and the lower plate 10 c are hermetically joined. A space (e.g., a “second space”) 11 b is formed between the plurality of grooves formed in the lower surface of the middle plate 10 b and the upper surface of the lower plate 10 c. In the middle plate 10 b, a large number of first gas-passages 12 a, which run from the space 11 a toward the lower plate 10 c through a plurality of holes formed in the middle plate 10 b, and a second gas-passage 12 b, which communicates not with the space 11 a but with the space 11 b, are formed. In the lower plate 10 c, a large number of first gas-discharging-holes 13 a, which communicate with the first gas-passages 12 a, and a large number of second gas-discharging-holes 13 b, which communicates with the space 11 b, are formed.

Herein, the inside diameter of each first gas-passage 12 a formed in the middle plate 10 b is for example 0.5 to 3 mm, preferably 1.0 to 2.0 mm. The inside diameter of each first gas-discharging-hole 13 a formed in the lower plate 10 c has a two-tier structure, wherein the diameter is for example φ1.0 to 3.5 mm, preferably φ1.2 to 2.3 mm, at a portion on the side of the space 11 a and for example φ0.3 to 1.0 mm, preferably φ0.5 to 0.7 mm, at the other portion on the side of the lower opening.

A first gas-introducing-pipe 14 a and a second gas-introducing-pipe 14 b are connected to an upper surface of the upper plate 10 a. The first gas-introducing-pipe 14 a communicates with the space 11 a. The second gas-introducing-pipe 14 b communicates with the second gas-way 12 b of the middle plate 10 b and the space 11 b. Thus, a gas introduced from the first gas-introducing-pipe 14 a is discharged out from the first gas-discharging-holes 13 a through the space 11 a and the first gas-passages 12 a. On the other hand, a gas introduced from the second gas-introducing-pipe 14 b is introduced into the space 11 b through the second gas-passage 12 b and then discharged out from the second gas-discharging-holes 13 b. That is, the showerhead 10 is a postmix type wherein the gas supplied from the first gas-introducing-pipe 14 a and the gas supplied from the second gas-introducing-pipe 14 b are independently supplied into the chamber 2. That is, the gas supplied from the first gas-introducing-pipe 14 a and the gas supplied from the second gas-introducing-pipe 14 b are not mixed in the showerhead 10, and supplied separately.

Herein, FIG. 7 is an enlarged view of the showerhead of FIG. 1. As shown in FIGS. 1 and 7, a sealing ring 10 h can be interposed between a lower surface of a portion of the upper plate 10 a surrounding a connecting portion with the second gas-introducing-pipe 14 b, which introduces the second process gas, and a flange 10 g at a portion of the middle plate 10 b forming the second gas-passage 12 b. Thus, it can be prevented more surely that the respective gases supplied from the first gas-introducing-pipe 14 a and the second gas-introducing-pipe 14 b mix with each other.

FIG. 8 is a sectional view taken along A-A line of FIG. 7, and FIG. 9 is a sectional view taken along B-B line of FIG. 7. In FIGS. 7 and 8, a numeral sign 101 indicates bolts. The bolts 101 fasten the middle plate 10 b and the lower plate 10 c. Arrows in FIG. 9 indicate flow directions of gas supplied from the second gas-passage 12 b into the space 11 b.

As shown in FIGS. 7 and 9, slits 212 b as gas-discharging-holes are formed on right and left sides at a lower end of the second gas-passage 12 b. The direction in which the slits 212 b are formed may be not only a right and left direction but also a vertical direction or a diagonal direction. Instead of the slits 212 b, discharging holes may be formed. The diameter of each discharging hole is preferably 1.0 to 3.0 mm, in particular 2.0 mm. The number of the discharging holes is optional.

On the other hand, as shown in FIG. 1, a flange 14 is commonly welded to respective base ends of the first gas-introducing-pipe 14 a and the second gas-introducing-pipe 14 b, which are connected to the upper plate 10 a. An insulating member 24 including a first gas-passage 24 a and a second gas-passage 24 b is connected to the flange 14. A gas introducing member 26 including a first gas-passage 26 a and a second gas-passage 26 b is connected to the other end of the insulating member 24. Then, the gas introducing member 26 is connected to an upper surface of the lid member 15. The lid member 15 and the chamber 2 have, respectively, a first gas-passage 15 a, 2 a and a second gas-passage 15 b, 2 b. The first gas-passages 24 a, 26 a, 15 a and 2 a and the second gas-passages 24 b, 26 b, 15 b and 2 b from the flange 14 to the chamber 2 are, respectively, communicated in series, and sealing rings such as O-rings are interposed at connecting portions thereof. In addition, a first gas pipe 25 a is connected to the first gas-passage 2 a in the chamber 2, and a second gas pipe 25 b is connected to the second gas-passage 2 b. And the respective base ends of the gas pipes 25 a and 25 b are connected to a gas supplying part 30 of gas-supplying mechanism 330 which supplies, for example, a process gas into the chamber through the showerhead.

The gas supplying mechanism or part 30 has: a ClF₃ gas source 31 that supplies ClF₃ gas, which is a cleaning gas; a TiCl₄ gas source 32 that supplies TiCl₄ gas, which is a film-forming gas; an Ar gas source 33 that supplies Ar gas, which is a carrier gas; a H₂ gas source 34 that supplies H₂ gas, which is a reduction gas; and a NH₃ gas source 35 that supplies NH₃ gas, which is used for nitriding a Ti film. The ClF₃ gas source 31, the TiCl₄ gas source 32 and the Ar gas source 33 are respectively connected to gas pipes 36, 37 and 38. The gas pipes 36, 37 and 38 are connected to the second gas pipe 25 b. The H₂ gas source 34 and the NH₃ gas source 35 are respectively connected to gas pipes 39, 40. The gas pipes 39 and 40 are connected to the first gas pipe 25 a.

The gas supplying part 30 has: a ClF₃ gas source 31 that supplies ClF₃ gas, which is a cleaning gas; a TiCl₄ gas source 32 that supplies TiCl₄ gas, which is a film-forming gas; an Ar gas source 33 that supplies Ar gas, which is a carrier gas; a H₂ gas source 34 that supplies H₂ gas, which is a reduction gas; and a NH₃ gas source 35 that supplies NH₃ gas, which is used for nitriding a Ti film. The ClF₃ gas source 31, the TiCl₄ gas source 32 and the Ar gas source 33 are respectively connected to gas pipes 36, 37 and 38. The gas pipes 36, 37 and 38 are connected to the second gas pipe 25 b. The H₂ gas source 34 and the NH₃ gas source 35 are respectively connected to gas pipes 39, 40. The gas pipes 39 and 40 are connected to the first gas pipe 25 a.

The respective gases from the H₂ gas source 34 and the NH₃ gas source 35 are introduced in the space 11 a of the showerhead 10, through the gas pipe 25 a, the first gas-passages 2 a, 15 a, 26 a and 24 a of the above respective members and the gas-introducing-pipe 14 a. Then, the respective gases are discharged out from the first gas-discharging-holes 13 a of the lower plate 10 c through the first gas-passages 12 a of the middle plate 10 b.

Therefore, during a film-forming process, the TiCl₄ gas and the H₂ gas are not mixed with each other on the way to be supplied, but mixed after discharged into the chamber 2. Plasma is generated, a predetermined reaction is produced, and a Ti film is deposited on the semiconductor wafer W. A mass-flow controller 41 and a pair of opening/closing valves 42 and 43, between which the mass-flow controller 41 is sandwiched, are provided in each gas pipe 36, 37, 38, 39, 40 from each gas source. The gas supplying part 30 includes an N₂ gas source, another pipe, and another opening/closing valve and so on, which are not shown. In addition, for example, the gases supplied into the spaces 11 a and 11 b may be changed by changing the gas sources connected to the first gas-passage 26 a and the second gas-passage 26 b, which are formed in the gas introducing member 26.

A lid member 15 having an opening is mounted on an upper side of the chamber 2. A circular insulating member 16 is mounted on an inside peripheral portion of the lid member 15. Then, the supporting portion 10 e of the upper plate 10 a is supported by the insulating member 16. An upper portion of the supporting portion 10 e is covered by a circular insulating member 21 for the purpose of heat insulation. The insulating member 21 is supported by the lid member 15. The insulating member 16 has an effect of electrical insulation between the showerhead 10 and the chamber 2 and an effect of heat (thermal) insulation. Sealing rings such as O-rings are respectively interposed between the chamber 2 and the lid member 15, between the lid member 15 and the insulating member 16, and between the insulating member 16 and the supporting portion 10 e. Thus, a sealed state is formed.

An inside heater 17 is arranged on an upper surface of the horizontal portion 10 d of the upper plate 10 a, correspondingly to the whole surface of the semiconductor wafer W placed on the pedestal 3. For example, the inside heater 17 may be formed by sandwiching a thin plate-like heater member between mica insulating plates. A circular (doughnut-like) outside heater 18, for example a sheath heater, is fitted so as to surround an outside periphery of the inside heater 17. (FIG. 14 shows a structure wherein the same heater as the inside heater 17 is arranged as an outside heater.) These heaters function as elements of a showerhead-temperature controlling unit, which is explained below.

A space 19 is provided above the inside heater 17. A heat insulating member 20 is arranged above the space 19. The heat insulating member 20 may be a ceramics resin such as Al₂O₃ or the like. The heat insulating member 20 has a cooling-gas passage 20 a and a discharging port 20 b. A dry-air supplying pipe 61 a for cooling an inside portion is connected to an upper portion of the cooling-gas passage 20 a. A dry-air supplying pipe 61 b for cooling an outside portion is arranged above the supporting portion 10 e of the upper plate 10 a. The pipe 61 b has a pipe portion 61 c along an inside periphery of the insulating member 21. A large number of jetting-holes for jetting out dry air are uniformly and downwardly provided at the pipe portion 61 c. The jetted dry air is supplied into a gap between the insulating member 16 and the heat insulating member 20 and its vicinity, so as to cool the outside heater and its vicinity.

A power supply line 45 is connected to an upper surface of the upper plate 10 a of the showerhead 10. The power supply line 45 is connected to a high-frequency electric power source 47 via a matching unit 46. Then, a high-frequency electric power is supplied from the high-frequency electric power source 47 to the showerhead 10. Thus, a high-frequency electric field is formed, the process gas supplied into the chamber 2 is made plasma, and the film-forming reaction is promoted.

A circular filler or infilling member 48 made of quartz is provided so as to prevent that plasma is generated around a lower portion of the showerhead 10, especially in a space surrounded by lateral surfaces of the upper plate 10 a, the middle plate 10 b and the lower plate 10 c, a lower surface of the insulating member 16, a lower surface of the lid member 15 and a side wall of the chamber 2. As shown in FIG. 3, the filler 48 has a concave portion 48 a at an outside portion thereof. Convex portions 49 a of a plurality of supporting members or fixing member 49 (shown fastened to the lid member 15 by means of screws) are fitted in the concave portion 48 a to support the filler 48. An elastic or resilient member 50 such as a fluoro rubber is interposed between a lateral surface of the concave portion 48 a of the filler 48 and a lateral surface of each convex portion 49 a of each supporting member 49. Because of the elastic member 50, centering of the showerhead 10 can be easily achieved and the filler 48 can be simply attached and removed. In addition, breakage of the filler 48 caused by thermal expansion and contraction can be prevented. An elastic or resilient member 51 is interposed between the filler 48 and the lid member 15, with the lid member 15 also functioning as a fixing member relative to the filler 48 therebelow. The elastic member 51 also has a function of preventing the breakage of the filler 48.

An exhaust pipe 52 is connected to a side wall at a base portion of the cylindrical pedestal supporting member 7 attached at a base portion of the chamber 2. An exhaust unit 53 is connected to the exhausting pipe 52. Thus, the chamber 2 can be evacuated. A unit that traps unreacted materials and/or by-products is not shown but provided on an upstream side with respect to the exhausting unit 53. The chamber 2 can be vacuumed to a predetermined vacuum level by driving the exhausting unit 53. In addition, a sealed box 23 is provided over the lid member 15. An exhausting port 54 is provided at an upper portion of the sealed box 23. Inside heated dry air and outside heated dry air in the sealed box 23 are adapted to be exhausted from the exhausting port 54.

The CVD film-forming apparatus 1 according to the embodiment has a showerhead-temperature controlling unit 60 that controls a temperature of the showerhead 10. The showerhead-temperature controlling unit 60 is explained hereinafter.

As main elements, the showerhead-temperature controlling unit 60 has: the inside heater 17 and the outside heater 18, which are described above as a heating mechanism; the dry-air supplying pipes 61 a and 61 b for supplying dry air as a cooling mechanism; a temperature-detecting mechanism consisting of thermocouples 65 a, 65 b, 66 a and 66 b that monitor temperatures of the inside heater 17, the outside heater 18 and the lower plate 10 d of the showerhead 10; and a controller 62 that controls the above elements.

As enlargedly shown in FIG. 4, an electric power source 63 is connected to the inside heater 17, and an electric power source 64 is connected to the outside heater 18. At a position corresponding to the inside heater 17 arranged at the inside portion on the upper plate 10 a of the showerhead 10, the thermocouple 65 a for detecting the temperature contacts with an insulating sheet 131 of high thermal conductivity on the upper plate, and the thermocouple 65 b contacts with the inside of the lower plate. At a position corresponding to the outside heater 18 arranged at the outside portion on the upper plate 10 a, the thermocouple 66 a for detecting the temperature of the outside portion of the upper plate 10 a contacts with the inside of the upper plate and the thermocouple 66 b for detecting the temperature of the outside portion of the lower plate 10 c contacts with the inside of the lower plate. Each thermocouple 65 a, 65 b, 66 a, 66 b may be a plurality of thermocouples. In addition, provided is an inside (e.g., “first” or “second”)-temperature controller 67 that controls the temperature by means of a PID control to the output of the inside heater 17, based on an instruction of the controller 62 and a signal detected by the thermocouple 65 a or 65 b, and provided is an outside (e.g., “first” or “second”)-temperature controller 68 that controls the temperature by means of a PID control to the output of the outside heater 18 or the like, based on an instruction of the controller 62 and a signal detected by the thermocouple 66 a or 66 b. Thus, when the showerhead 10 is heated, temperature control of the showerhead 10 can be achieved by the temperature controllers 67 and 68.

On the other hand, the dry air supplied from the dry-air supplying pipe 61 a is introduced into the space 19 through the cooling-gas passage 20 a of the heat insulating member 20, as a cooling material. The dry air takes heat emitted from the inside heater 17 into the space 19, flows through the exhausting port 20 b, and is exhausted from the exhausting port 54 of the sealed box 23 provided on the upper portion of the lid member 15. The dry air supplied from the dry-air supplying pipe 61 b is discharged out from the discharging-holes on the lower side of the pipe, takes heat in the outside portion of the showerhead including the outside heater 18 or the like, and is exhausted from the exhausting port 54 of the sealed box 23. Air operation valves 69 a and 69 b are respectively provided in the dry-air supplying pipes 61 a and 61 b. The air operation valves 69 a and 69 b are controlled by the controller 62.

When the showerhead is heated while the showerhead controlling unit 60 is used, a preferable temperature control can be achieved in accordance with a control shown in FIG. 5. In the control shown in FIG. 5, a set temperature is set at the controller 62. Then, the temperature controller 67 controls the output of the inside heater 17 in such a manner that a temperature detected by the thermocouple 65 a or 65 b coincides with the set temperature. The value detected by the thermocouple 65 a or 65 b is also outputted to the temperature controller 68 via the controller 62. Then, the temperature controller 68 controls the output of the outside heater 18 in such a manner that the difference between a temperature detected by the thermocouple 66 a or 66 b at the position corresponding to the outside heater 18 and a temperature detected by the thermocouple 65 a or 65 b at the position corresponding to the inside heater 17 coincides with zero. Therefore, the temperature of the outside portion of the showerhead 10 and the temperature of the inside portion of the showerhead 10 are controlled to be substantially the same.

The upper surface of the upper plate 10 a of the showerhead 10 and a portion above it are exposed to atmospheric air. The thermocouples 65 b and 66 b of the showerhead-temperature controlling unit 60 are arranged in the showerhead, which can be a vacuum. However, the other elements are arranged in the atmospheric air.

In addition, as shown in FIG. 2, the showerhead 10 can be inverted outwardly from the chamber 2 by an inverting mechanism 80 having a hinge mechanism. Thus, as shown in FIG. 6, the showerhead 10 can be positioned substantially completely outside the chamber 2 in such a manner that the gas-discharging surface is directed upward. Thus, maintenance of the showerhead 10 can be very easily conducted. Concretely, from the state shown in FIG. 6, the plurality of supporting members 49 can be easily taken out outwardly by removing the fastening screws (arrow (1)). After the supporting members 49 are taken out, the filler 48 can be easily taken out upwardly (arrow (2)). Then, after the filler 48 is taken out, maintenance of the showerhead 10 itself can be conducted. For example, the lower plate 10 c and the middle plate 10 b can be easily taken out upwardly (arrow (3)). After the showerhead 10 is inverted, it is preferable that the showerhead 10 is held at a position inverted by 180 degrees. It is sufficient that the inverted degrees are around 180 degrees. In order to hold the showerhead 10 at such position, a gas spring or the like can be used.

Next, a processing operation of the CVD film-forming apparatus 1 as structured above is explained. At first, before a Ti thin film is formed on a semiconductor wafer W, a pre-coated film is formed on the surfaces of the showerhead 10 and the pedestal 3 and so on in accordance with the following steps. First, environs of the chamber 2, the heater 6 of the pedestal 3, and the inside and outside heaters 17 and 18 of the showerhead 10 are heated. Then, the chamber 2 is exhausted by the discharging unit 53, a predetermined gas is introduced into the chamber 2 at a predetermined flow rate, and the inside of the chamber 2 becomes a predetermined pressure. Then, a film-forming gas, which includes H₂ gas, TiCl₄ gas and other gases, is introduced into the chamber 2 at a predetermined flow rate, and a high-frequency electric power is supplied from the high-frequency electric power source 47 to the showerhead 10, so that plasma is generated in the chamber 2. Thus, a Ti film is deposited on the showerhead 10 and the pedestal 3 and so on. Then, the supply of the electric power from the high-frequency electric power source 47 and the supply of the TiCl₄ gas are stopped. Then, NH₃ gas and other gases are supplied at predetermined flow rates, and again the high-frequency electric power is supplied from the high-frequency electric power source 47 to the showerhead 10, so that plasma is generated. Thus, a surface of the deposited Ti film is nitrided, so that a stable pre-coated film is formed on the showerhead 10 and pedestal 3 and so on. After the nitriding process is completed, the supply of the electric power from the high-frequency electric power source 47 and the supply of the NH₃ gas are stopped.

After the pre-coating process is completed, a gate valve not shown is opened, and a semiconductor wafer W is conveyed into the chamber 2 and placed onto the pedestal 3. Then, the H₂ gas, the Ticl₄ gas and the other gases are supplied at predetermined flow rates, and a high-frequency electric power is supplied from the high-frequency electric power source 47 to the showerhead 10, so that plasma is generated in the chamber 2. Thus, a Ti film is deposited on the semiconductor wafer W. Then, the supply of the electric power from the high-frequency electric power source 47 and the supply of the TiCl₄ gas are stopped. Then, the NH₃ gas and the other gases are supplied at predetermined flow rates, and again the high-frequency electric power is supplied from the high-frequency electric power source 47 to the showerhead 10, so that plasma is generated. Thus, the Ti film deposited on the semiconductor wafer W is nitrided. After the nitriding process is completed, the supply of the electric power from the high-frequency electric power source 47 and the supply of the NH₃ gas are stopped. After the film-forming process is completed as described above, the processed semiconductor wafer W is conveyed out from the chamber 2, another semiconductor wafer W to be successively processed is conveyed into the chamber, and the same film-forming process is conducted to the latter semiconductor wafer W.

After the film-forming process is conducted to a predetermined number of semiconductor wafers W, the pedestal 3 and the showerhead 10 are cooled to a predetermined temperature, and ClF₃ gas as a cleaning gas is supplied into the chamber 2 in order to conduct a cleaning process.

In the series of processes, in accordance with the embodiment, the following effects can be achieved because the showerhead 10 is provided with the showerhead-temperature controlling unit 60.

In the pre-coating process and the film-forming process, unreacted products TiCl_(x) (x=1, 2, 3) may be formed. The TiCl_(x) has to be volatilized in order to form a stable film on the showerhead. For that purpose, a temperature not lower than 425° C., preferably not lower than 500° C., is necessary. As the conventional showerhead is passively heated by the heater in the pedestal, there is no certification of that the conventional showerhead is heated to or over 425° C. Thus, conventionally, there were possibilities that a stable pre-coated film may not be formed on the showerhead. However, in the embodiment, the showerhead 10 is provided with the showerhead-temperature controlling unit 60, so that the showerhead 10 can be actively heated to or over 425° C. In addition, by supplying a gas including the NH₃ gas so as to reduce and nitride TiCl_(x), a stable pre-coated film can be surely formed on the showerhead 10.

In addition, when the inside of the chamber 2 is heated to a film-forming temperature, if the showerhead 10 is heated only by radiant heat from the pedestal 3 like a conventional manner, it takes a long time for the temperature of the showerhead 10 to become stable at a predetermined heating temperature. However, according to the embodiment, in addition to being passively heated by the heater 6 of the pedestal 3, the showerhead 10 is in advance actively heated by the heaters 17 and 18 that are elements of the showerhead-temperature controlling unit 60. Thus, within a shorter time, the whole showerhead 10 is heated, so that the temperature of a surface of the lower plate of the showerhead 10 can be stabilized to a constant temperature. Thus, the temperature in the chamber 2 can be stabilized to a predetermined temperature within a short time. As described above, as the temperature of the showerhead 10 is controlled uniformly, the Ti film can be formed uniformly on the semiconductor wafer W. Especially, when a semiconductor wafer is enlarged to 300 mm and thus the apparatus is also enlarged, the above effect is remarkable.

During an idling state, the high-frequency electric power source is turned off. Thus, conventionally, in order to maintain the temperature of the showerhead 10 at a predetermined temperature, the temperature of the heater in the pedestal was set higher. On the other hand, according to the embodiment, as the temperature of the showerhead 10 is controlled by the showerhead-temperature controlling unit 60, the temperature of the showerhead 10 can be maintained and stabilized at a predetermined temperature, even during an idling state.

For a cleaning process, the temperature of the showerhead 10 has to be lowered from the film-forming temperature to a cleaning temperature of 200 to 300° C. Conventionally, heat-radiating performance of the showerhead was so poor that it took a long time for the temperature to fall down. However, according to the embodiment, dry air as a cooling medium is supplied to the upper portion of the showerhead 10 through the dry-air supplying pipes 61 a and 61 b by the showerhead-temperature controlling unit 60, in order to cool the showerhead. Thus, the inside temperature of the chamber 2 can be fast lowered to a cleaning temperature.

In the unit of the embodiment, the upper part of the upper plate 10 a of the showerhead 10 is exposed to atmospheric air. Thus, almost all the elements of the showerhead-temperature controlling unit 60 can be disposed inside atmosphere. Therefore, it is easy to handle the showerhead-temperature controlling unit 60.

In addition, in the embodiment, the inside heater 17 and the outside heater 18 are provided as a heating mechanism of the showerhead-temperature controlling unit 60, in order to achieve a two-zone control. Then, as shown in FIG. 4, the output of the inside heater 17 is controlled by the temperature controller 67 in such a manner that a temperature detected by the thermocouple 65 a or 65 b coincides with a set temperature, and the output of the outside heater 18 is controlled by the temperature controller 68 in such a manner that the difference between a temperature detected by the thermocouple 66 a or 66 b located correspondingly to the outside heater 18 and the temperature detected by the thermocouple 65 a or 65 b located correspondingly to the inside heater 17 coincides with zero, so that the inside portion and the outside portion of the showerhead 10 are controlled to be always at the same temperature. Thus, heat dissipation from the outside portion of the showerhead 10 can be inhibited, so that temperature controlling performance can be enhanced. Especially, when the size of a semiconductor wafer is enlarged to 300 mm, as heat tends to be dissipated from the outside portion of the showerhead 10, the above two-zone control is more effective.

At the maintenance of the showerhead 10, the showerhead 10 is inverted outwardly from the chamber 2 by the inverting mechanism 8. Thus, as shown in FIG. 6, the maintenance of the showerhead 10 can be conducted while the gas-discharging surface of the showerhead 10 is directed upward. That is, the maintenance of the showerhead 10 can be conducted very easily. Concretely, from the state shown in FIG. 6, the plurality of supporting members 49 are taken out outwardly. Then, the filler 48 is taken out upwardly. Then, the lower plate 10 c and the middle plate 10 b of the showerhead 10 are taken out upwardly. As described above, each operation for taking-out each element is so easy that the maintenance of the showerhead 10 can be conducted very easily.

This invention is not limited to the above embodiment, but may be variably modified within a scope of spirit of the invention. For example, although the film-forming process of a Ti film is explained in the above embodiment, this invention is not limited thereto, but applicable to a CVD film-forming process of another film such as a TiN film. In addition, although the case wherein the plasma is generated is explained, the plasma is not necessary. The showerhead-temperature controlling unit is also not limited to the above structure. The controlling method is also not limited to the above method. For example, although the dry air is used as a cooling medium, another gas such as Ar or N₂ can be also used. If plasma is not used, liquid such as water or coolant can be used as a cooling medium. In addition, although the process to the semiconductor wafer is explained, this invention is not limited thereto, but also applicable to a process to another substrate such as a Liquid-Crystal-Display glass substrate.

Next, a variant of the above embodiment is explained in detail.

As shown in FIG. 9, in the above embodiment, the second gas-supplying portion 12 communicating with the second gas-passage 12 b is arranged in the substantially central portion of the space 11 b formed below the middle plate. The openings 12 c are formed on the lateral sides of the gas-supplying portion 12. Thus, the gas supplied through the second gas-passage 12 b, which communicates with the second gas-supplying pipe 14 b and is formed above the middle plate, is discharged from the openings 12 c of the gas-discharging portion 12 and directly diffused into the space 11 b.

However, according to that manner, the gas supplied through the second gas-passage 12 b may not be sufficiently uniformly diffused into the space 11 b of the middle plate 10 c.

Then, it is preferable that one or more gas-diffusion promoting pipes are connected to the openings 12 c of the second gas-discharging portion 12 arranged in the substantially central portion of the space 11 b.

In the case of the middle plate 10 c shown in FIG. 10, a substantially H-shaped gas-diffusion promoting pipe 110 is arranged in the space 11 b below the middle plate 10 c in order to uniformly diffuse the second gas. The central portion of the substantially H-shaped gas-diffusion promoting pipe 110 is connected to and fitted in the second gas-discharging portion 12. Gas-discharging holes 110 a are formed at four tip portions of the gas-diffusion promoting pipe 110. The gas-diffusion promoting pipe 110 is formed integratedly by welding. Supporting pillars 110 b that supports the gas-diffusion promoting pipe 110 are fixed to the middle plate 10 b and the upper surface of the lower plate 10 c, in order to prevent motion of the gas-diffusion promoting pipe 110.

In this case, the gas-discharging holes 110 a formed at the respective tip portions are open toward the upper plate, so that the gas supplied through the second gas-discharging portion 12 can be sufficiently uniformly diffused into the space 11 b. Arrows in FIG. 10 schematically show flows of the gas supplied from the gas-discharging holes 110 a into the space 11 b. The shape, the orientation and the position of the gas-diffusion promoting pipe 110, the number of gas-discharging holes 110 a and the manner of openings are not limited, if the gas supplied through the second gas-passage 12 b can be diffused sufficiently uniformly into the space 11 b. For example, the gas-discharging holes 110 a may be formed to open to a lateral direction. The gas-discharging holes 110 a may be formed uniformly on the way to the tip ends of the pipe, preferably uniformly in the space 11 b.

FIG. 11 shows a sectional view of the middle plate 10 b attached to the lower plate 10 c and the gas-diffusion promoting pipe 110 shown in FIG. 10. FIG. 11 shows a section piercing a central pipe 110 c of the gas-diffusion promoting pipe 110 basically, but shows a section piercing a gas-discharging hole 110 a at a right-end portion of the gas-diffusion promoting pipe 110.

FIGS. 12 and 13 show a variant regarding the control system. FIG. 12 is a schematic view showing the variant at a portion corresponding to the heating mechanism of FIG. 4, and FIG. 13 is a view showing the variant of the controlling manner of FIG. 5.

In the case shown in FIGS. 12 and 13, noise filters 120 are provided between the control system and the respective thermocouples 65 a, 65 b, 66 a and 66 b, and between the control system and the respective heaters 17 and 18. Preferably, they are arranged nearer to the control system. Providing the noise filters 120 like this is effective in removing noises from the high-frequency electric power source 47 to improve the controlling performance.

In a variant shown in FIG. 14, instead of the circular outside heater 18 having a circular section, a flat doughnut-like outside heater 118 is provided. Like this, the shape of the heater is not limited in particular.

In the variant shown in FIG. 14, an insulating member or sheet 131 is formed between the inside heater 17 and the upper plate 10 a, and an insulating member or sheet 132 is similarly formed between the outside heater 118 and the upper plate 10 a. The thickness of the respective insulating sheets 131 is a degree not affected by noises, for example 0.5 mm to 1.0 mm. The upper plate 10 a functions as an electrode for generating plasma, so that the insulating sheets 131 and 132 are preferably thick in order to inhibit effects of the noises that the heaters receive. Herein, the insulating sheets 131 and 132 have to have high heat conductivity and high heat resistance. Thus, ceramics such as aluminum nitride is suitable as a material of the insulating sheets 131 and 132.

In a variant shown in FIG. 15, instead of the elastic member 50 made of a fluorine rubber or the like, a corrosion-resisting metal spring, for example an elastic or resilient member 150 made of a Ni-alloy such as inconel, is provided. Like this, the manner of an elastic member interposed between the lateral surface of the concave portion 48 a of the filler 48 and the lateral surface of the convex portion 49 a of the supporting member 49 is not limited in particular.

Herein, regarding during the idling state and during the cleaning process, the respective features of temperature control according to this invention and prior art are shown in the following table.

Temperature of Temperature of showerhead pedestal Operation Prior art 470~480° C. 640~650° C. Temperature of pedestal has to be raised not lower than film-forming temperature Invention 500° C. 640° C. Temperature of showerhead is directly controlled 

1. A film-forming apparatus comprising: a processing container that defines a chamber, a pedestal arranged in the chamber, on which a substrate to be processed can be placed, a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes, a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead, a showerhead-temperature controlling unit that controls a temperature of the showerhead, and an inverting mechanism that inverts the showerhead by turning the showerhead outwardly from the chamber, the showerhead comprising a horizontal portion and a supporting portion extending upward from a peripheral region of said horizontal portion, said supporting portion having an interior wall surface extending upward from said horizontal portion to define, together with said horizontal portion, a cavity, said showerhead further comprising ribs extending radially inward from said interior wall surface into said cavity.
 2. A film-forming apparatus according to claim 1, further comprising: a heat insulating member arranged on or above an atmospheric space on the showerhead so as to cover the showerhead.
 3. A film-forming apparatus according to claim 1, wherein the showerhead-temperature controlling unit includes: a heating mechanism that heats the showerhead, a cooling mechanism that cools the showerhead, a temperature-detecting mechanism that detects a temperature of the showerhead, and a controller that controls at least the heating mechanism, based on a result detected by the temperature-detecting mechanism.
 4. A film-forming apparatus according to claim 1, further comprising: an insulating member arranged on a showerhead body of the showerhead and inside a supporting part of the showerhead.
 5. A film-forming apparatus according to claim 1 wherein said ribs extend radially inward an equal distance and said heat insulating member is positioned radially internally of said ribs such that said heat insulating member is radially spaced inward of the interior surface of said cylindrical wall relative to said ribs.
 6. A film-forming apparatus according to claim 1, further comprising a circular insulating member arranged between the showerhead and the chamber.
 7. A film forming apparatus according to claim 1, further comprising a heat insulating member received in said cavity and a heater, supported on said horizontal portion, and wherein a space is formed between an upper surface of said heater and a lower surface of said heat insulating member.
 8. A film-forming apparatus comprising: a processing container that defines a chamber, a pedestal arranged in the chamber, on which a substrate to be processed can be placed, a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes, a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead, a showerhead-temperature controlling unit that controls a temperature of the showerhead, and an insulating member arranged on a showerhead body of the showerhead and outside a supporting part of the showerhead wherein the showerhead has: a heat insulating member arranged in an atmospheric space, with the atmospheric space being on or above the showerhead so as to cover the showerhead, a cooling mechanism that cools the atmospheric space so as to cool the showerhead, a heating mechanism that heats the showerhead, a temperature-detecting mechanism that detects a temperature of the showerhead, a controller that controls at least the heating mechanism, based on a result detected by the temperature-detecting mechanism, an upper plate, a middle plate, and a lower plate having the discharge holes which open out into the chamber to discharge gas from said showerhead, and the showerhead further comprising radially-extending thermally transmitting components between the insulating member and the supporting part of the showerhead.
 9. A film-forming apparatus according to claim 8, wherein the heating mechanism has: an inside heater that heats an inside portion of the showerhead, and an outside heater that heats an outside portion of the showerhead, and the temperature detecting mechanism has: an inside-temperature detecting part that detects a temperature of the inside portion, and an outside-temperature detecting part that detects a temperature of the outside portion.
 10. A film-forming apparatus according to claim 8, further comprising a plasma-generating unit for generating plasma of the process gas in the chamber.
 11. A film-forming apparatus according to claim 8, further comprising: an inverting mechanism that inverts the showerhead by turning the showerhead outwardly from the chamber.
 12. A film-forming apparatus according to claim 8, further comprising: a circular filler and a fixing member for fixing the filler to the showerhead or the processing container arranged between the showerhead and the processing container.
 13. A film-forming apparatus according to claim 8, the heating mechanism has: an inside heater that heats an inside portion of the showerhead, and an outside heater that heats an outside portion of the showerhead.
 14. A film-forming apparatus comprising: a processing container that defines a chamber, a pedestal arranged in the chamber, on which a substrate to be processed can be placed, a showerhead provided opposite to the pedestal, which has a large number of gas-discharging holes, a gas-supplying mechanism that supplies a process gas into the chamber through the showerhead, a showerhead-temperature controlling unit that controls a temperature of the showerhead, and a plasma-generating unit for generating plasma of the process gas in the chamber, the showerhead comprising a horizontal portion and a supporting portion extending upward from a peripheral region of said horizontal portion, said supporting portion having an interior wall surface extending upward from said horizontal portion to define, together with said horizontal portion, a cavity, said showerhead further comprising ribs extending radially inward from said interior wall surface into said cavity. 